Generally, in gas chromatography ("GC"), a sample to be analyzed is introduced as a pulse of gas in a stream of carrier gas into a chromatographic column. A separation process takes place in the column, and at the end of the column the individual components of the sample will emerge more or less separated in time. The individual components separated by the column are detected by continuously monitoring some physical or chemical property of the effluent.
Ideally, each component in the sample emerges from the column at different times so that, at any one time, the gas flowing into the detector is either all carrier gas or a combination of carrier gas and one of the components of the sample. The detector functions by producing a signal related to the change in the intensity of a given characteristic of the gases flowing through it. As each sample component passes through the detector, the output signal varies from the value it has when the detector is full of carrier gas, with the amount of variation depending on the concentration of the sample component and typically being in the form of a spike or peak on a steady signal. A widely used detector is the thermal conductivity detector (also referred to as a hot wire detector or katharometer) which measures the difference between the thermal conductivity of the pure carrier gas and the mixture of the sample component and the carrier gas.
An injector is also part of a GC system, for introducing the short pulse of a sample gas to be analyzed into carrier gas before the column. Conventional injectors involve the use of a syringe for providing a measured volume of sample.
A miniaturized GC system is disclosed in a report "A Prototype Gas Analysis System Using a Miniature Gas Chromatograph" by J. H. Jerman, S. C. Terry and S. Saadat, Stanford University (June 1, 1980), and in an article "Silicon as a Mechanical Material" by K. E. Petersen, Proc. IEEE 70, 420-457 (May 1982). The techniques of integrated electronic circuit processing are utilized to form the main components of a GC system. A capillary column is formed by etching and laminating wafers of silicon and glass. A valve for the injector comprises a mechanical solenoid plunger and a nickel diaphragm. A volume of sample gas is injected through a capillary by computerized coordination of pressures. A hot wire thermal detector is formed with a thin-film nickel resistor on a thin glass membrane in a cavity.
An improved valve for such a system is disclosed in "A Microminiature Electric-to Fluidic Valve" by M. J. Zdeblick and J. B. Angell, Transducers 87, pp 827-829 (1987). The valve utilizes a sealed cavity filled with a liquid. One wall of the cavity is formed with a flexible membrane which can press against a pneumatic nozzle. When the liquid is heated, it's pressure increases, pushing the membrane toward the nozzle, turning it off.
Although the aforementioned background reflects advancements in miniaturized devices including GC systems, further improvements are quite desirable to increase reliability and precision of operation and also to simplify manufacturability of parts. There also are requirements to reduce even further size, weight, and electrical consumption of instruments for applications such as for aerospace where they are at a premium.
Therefore an object of the present invention is to provide an improved unitary device such as for gas chromatography device, particularly a device of the type utilizing a plurality of wafer members laminated together, having increased flexibility, reliability, speed and precision of operation. Further objects are to provide improved components in such a device, including unique gas chromatographic column structures, sample gas injectors, and detectors.
Another object is to provide an improved gas valve in a unitary body. Yet other objects are to provide an improved gas detector system and to provide a unique structural material for a miniature device.